A unique coagulation enzyme has been isolated from malignant tissue, purified to homogeneity and partially characterized. This enzyme, cancer procoagulant, has been tentatively shown to be a sulfhydryl protease that initiates clotting by directly activating factor X in the coagulation cascade. Studies of the enzymatic activity of cancer procoagulant have demonstrated that it is present in serum free medium and extracts of malignant tissue but not in the same type of samples from normal tissues. We are continuing to study the physical, chemical and enzymatic properties of this enzyme. In addition, we are studying the role of this enzyme in the malignant process by determining its role in tumorigenicity and in the metastatic capacity of malignant cells. We have developed an antibody to cancer procoagulant and an immunoassay for the enzyme will be developed.